In a release published Tuesday, the court's Judge John Bates wrote the potential damage of disclosing the opinions is "real and significant, and, quite frankly, beyond debate," as it could allow enemies to avoid detection and circumvent U.S. intelligence, The New York Times reported.

Bates' statement was in a response to a request by the American Civil Liberties Union on two rulings in January and May on the National Security Agency's program of wiretapping without warrants.

However, Bates said he agreed with the ACLU's claim that "enhanced public scrutiny could provide an additional safeguard against mistakes, overreaching and abuse."

The court was created in 1978 to oversee requests for warrants to spy on suspected foreign intelligence agents inside the United States.

Jameel Jaffer, director of the National Security Project at the ACLU, told the Times he was disappointed.

"A federal court's interpretation of federal law should not be kept secret," Jaffer said.